Normally what is the last layer of mat used before fairing the glass?

Discussion in 'Fiberglass and Composite Boat Building' started by midcap, Jun 29, 2015.

  1. midcap
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    midcap Junior Member

    I would like to know what you guys normally use as the last layer of glass before pulling fairing compound and blocking it out. It seems like I could do it with my 1708 but I don't want to cut into the mat while sanding.

    I was thinking about laying down some 1.5oz CSM over my last layer of 1708 for my deck.
     
  2. upchurchmr
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    upchurchmr Senior Member

    Are you using epoxy or polyester?
    No mat with epoxy.
     
  3. rwatson
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    rwatson Senior Member

    I would have thought that Matt as the final layer is just heavier fairing compound.
     
  4. midcap
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    midcap Junior Member

    Probably vinyl ester
     
  5. PAR
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    PAR Yacht Designer/Builder

    Cutting into the mat while sanding is a whole lot less problematic, than abating the cloth. 1708 will offer a pretty darn heavy mat to have to fair, so burning through it while sanding will be rare.
     
  6. midcap
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    midcap Junior Member

    What would you reccomend? On the top before I put down non skid and on the bottom to seal it up?

    I'm at the point where I am seriosly considering going 1/2" coosa instead of ply and be done with it.
     
  7. rwatson
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    rwatson Senior Member

    You still have to put glass on the outside dont you ?

    PS in the info sheet
    "Typical applications include marine: transoms,
    stringers, bulkheads, hatch lids and decking;
    industrial: wall panels, museum exhibits, cabinetry
    and instrument/transport cases; transportation:
    floors"

    Why dont they mention hull panels ?
     
    Last edited: Jul 1, 2015
  8. PAR
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    PAR Yacht Designer/Builder

    On alternating mat/cloth schedules, I like a light mat out, if possible over a finish cloth, assuming a heavy rove or cloth is below. It helps prevent print through and offers a resin rich surface to work with while fairing. Unless you hull is quite unfair, don't worry so much about cutting into the mat, as the mat doesn't offer any strength, just a place for the resin to settle.
     
  9. keysdisease
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    keysdisease Senior Member

    A friend made a Crowther Bucaneer 40 out of foam sandwich. He was a very experienced glass man and was extremely careful that his layup was perfect. He used a tight weave (approx. 3/8") roving as his final and then used the "high" points as his fairing guide. Worked slicker than poo.

    :cool:
     
  10. midcap
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    midcap Junior Member

    you are correct, but I don't have to worry about the bottom and I would just lay down some mat before I put down the non skid coating. So I wouldn't have to glass the bottom and that would save me time and materials while giving me a rot free core, but at 4 times the price. I can get a 1/2" sheet of coosa for 200 locally where as the Marine Tech treated ply is $50 locally. Despite the marine tech not rotting, it still may retain moisture and is about twice the weight of coosa.
     
  11. midcap
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    midcap Junior Member

    Thanks, so I imagine if I laid down one layer of 1708 and then a layer of 1.5oz csm on top that would be plenty enough if I am painting on top and putting non skid where traffic will be?
     
  12. PAR
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    PAR Yacht Designer/Builder

    Yep, and I'll add you only need the light mat if the surface is particularly unfair and you have to knock down a lot. If the hull is pretty lumpy the extra course of mat offers something to grind into, without damaging any structural fabrics. If it was me, I'd do a quick long boarding and see how deep the worst of it is. You can treat these areas locally, or just skin the whole hull with something to grind off.
     
  13. midcap
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    midcap Junior Member

    that makes a lot of sense. Thanks.

    As for the bottom of the ply facing the bilge, a layer of 1708 would be fine or probably overkill?
     
  14. PAR
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    PAR Yacht Designer/Builder

    Unless you expect to have lots of nuts and bolt rolling around down there, probably over kill. In these places 'glass isn't the best choice, think modi-acrylic or polyester fabric instead, for the much improved abrasion resistance.
     

  15. midcap
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    midcap Junior Member

    I meant the the underside of the plywood that i would use as a core for the deck which sits on top the stringers to seal out moisture and stop the panel from warping.

    Sorry my other post was hard to follow.
     
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